Astronomers will study 250,000 distant galaxies for clues to origins of the universe

With time running out for the Hubble Space Telescope, astronomers in Baltimore and around the world are gearing up for the biggest research project ever mounted on the orbiting observatory.

Later this year, astronomers from dozens of institutions will begin gathering images of more than 250,000 of the most distant galaxies in the universe. They will seek answers to some of astronomy's biggest questions - queries that go to the origins of the universe itself.

There is a sense of urgency to the effort. Nearly 20 years after it was launched into orbit, the Hubble telescope is working better than ever, but the most recent repair mission was its last. A breakdown could hobble or end the scientific work at any time.

"What's really crucial now is to look forward to the fact that we won't have Hubble in a few years," said Sandra Faber, chair of astronomy at the University of California Santa Cruz and a principle investigator on the new project.

"We don't want [future] generations to say, 'Those guys were so stupid. ... They never really tackled the big questions.' We don't want to look stupid," she said during a recent visit to the Space Telescope Science Institute in Baltimore, which manages Hubble science.

The scientists, more than 90 of them, have been awarded an unprecedented amount of Hubble use for the work. It works out to more than 900 orbits. That's 3 1/2 months, or roughly 10 percent of Hubble's total observing time over three years.

The data they gather, combined with pictures and information gathered by other observatories, is expected to be mined long after the Hubble is retired, as researchers work to piece together the early evolution of the first stars and galaxies, and of the expanding universe itself.

The mammoth undertaking is part of the Hubble Multi-Cycle Treasury Program. It's being launched now because the space telescope, in many respects, is in the prime of its life.

Last May, astronauts replaced its failing gyroscopes and batteries, and installed the Hubble's most powerful workhorse camera ever, the Wide Field Camera 3 (WFC3, pronounced Whiff-see 3). They also repaired the Advanced Camera for Surveys (ACS), which is ideally suited for cataloging objects at vast distances, such as a peculiar kind of exploding star known as a Type Ia supernova.

But while the telescope is working better than ever, last May's house call was NASA's final servicing mission to the Hubble. The shuttle fleet is being retired.

Some of the scientific questions that remain are "ridiculously important, big ones," Faber said. "That's why they haven't been done up to now."

The committee that reviews and approves requests for observing time on the Hubble asked astronomers for proposals that could "accomplish multiple scientific goals that would be a lasting legacy of the telescope, that would have an enduring use," said Henry Ferguson of the Space Telescope Science Institute.

Scientists responded with 39 proposals, seeking 15 times more telescope time than was available. The committee selected three, one of which merged Faber's ideas with a similar proposal submitted by Ferguson.

Their combined objectives are ambitious, Ferguson said. They include "trying to get a handle on how dark energy is behaving, how the acceleration of the universe happened [and] studying the earliest galaxies."

Faber said project scientists will seek their answers amid galaxies in five regions of the sky, areas that astronomers have named Hubble Deep Field, Ultra Deep Field, GOODS, COSMOS and Extended Groth Strip.

The target areas were chosen because they are outside the plane of our own spiral Milky Way galaxy, and therefore relatively empty of nearby stars. Each is a kind of an open window to the farthest reaches of the universe.

These are the fields "in which extra-galactic astronomy can really concentrate and pound away," Faber said. "We have established the touchstone fields that will carry us possibly for centuries, certainly decades."

Ferguson calls them "deep watering holes," where the Hubble, Spitzer, Chandra and Herschel space telescopes have gathered data in a variety of wavelengths of light - information that will complement and support Hubble's new observations.

As important as they have become, these star fields constitute just a tiny fragment of the sky, barely an eighth of the area covered by a full moon. But they contain hundreds of thousands of far-off galaxies, a critical factor for astronomers.

"You need hundreds of thousands, if not millions of objects - galaxies and stars - to be able to do the statistical tests that will say whether we're really understanding how galaxies evolved, how the universe is expanding," Ferguson said.

That's because galaxies change far too slowly to allow astronomers to follow a single example as they might a single child, taking pictures as it's born and grows. They can only see snapshots of hundreds of thousands of galaxies, showing what each one looked like at just one moment in its evolution.